Equalized capacitive touchpad and touch positioning method

ABSTRACT

An equalized capacitive touchpad and a touch positioning method for a capacitive touchpad use an equalizer to correct a sensed value of a mutual capacitance between two sensing lines of the capacitive touchpad, to thereby offset the attenuation of the sensed value due to the impedance of the two sensing lines. Thus, the sensed values generated from different positions along a sensing line are equalized, and the touch positioning accuracy of the capacitive touchpad is improved.

CROSS REFERENCE TO RELATED APPLICATION

This application is a continuation-in-part of U.S. patent applicationSer. No. 12/382,764, filed 24 Mar. 2009, and entitled “EqualizedCapacitive Touchpad and Touch Positioning Method,” the disclosure ofwhich is hereby incorporated by reference as if set forth fully herein.

FIELD OF THE INVENTION

The present invention is related generally to a capacitive touchpad and,more particularly, to an equalized capacitive touchpad and a touchpositioning method for a capacitive touchpad.

BACKGROUND OF THE INVENTION

Traditionally, the touch sensor of a capacitive touchpad is realized bya printed circuit board (PCB). However, the opaqueness of the PCBrestricts applications of the capacitive touchpad in cell phones,personal digital assistants (PDAs), multi-media display panels and otherelectronic products. Transparent electrically conductive films, such asindium tin oxide (ITO) and indium zinc oxide (IZO), can be used toreplace the PCB traces for transparent applications. Alternatively, atransparent membrane printed with conductive carbon paste or silver inktrances may implement applications of a capacitive touchpad forelectronic products where the touchpad is intended to reveal through abottom side thereof. However, unlike the PCB trace whose impedance is solow as to be negligible, the trace made of ITO, IZO, conductive carbonpaste, silver ink or the like exhibit a significant impedance, whichwill result in errors in sensed values of the touch sensor anddisadvantageously affect touch positioning by the capacitive touchpad.As shown in FIG. 1, a capacitive touchpad 100 includes a touch sensor110 and a controller 120. The touch sensor 110 shown therein is atwo-dimensional one, which has sensing lines arranged in two directions,namely the group of X1, X2, . . . , Xm, . . . , XM and the group of Y1,Y2, . . . , Yn, . . . , YN. Typically, the two directions of the sensinglines are referred to as X direction and Y direction for convenience'ssake. If the touch sensor 110 is realized by a PCB, the sensing linesX1, X2, . . . , Xm, . . . , XM and Y1, Y2, . . . , Yn, . . . , YN arecopper traces on the PCB. If, for transparent applications, ITO or IZOis used to make the sensing lines X1, X2, . . . , Xm, . . . , XM and Y1,Y2, . . . , Yn, . . . , YN, then the substrate for the sensing lines canbe made of glass, plastic or other transparent materials. If the sensinglines X1, X2, . . . , Xm, . . . , XM and Y1, Y2, . . . , Yn, . . . , YNare conductive carbon paste or silver ink, the substrate is atransparent membrane. The controller 120 is a semiconductor chipinstalled on a flexible printed circuit board (FPC) 115, and isconnected to the sensing lines X1, X2, . . . , Xm, . . . , XM and Y1,Y2, . . . , Yn, . . . , YN by metal wires 125 printed on the FPC 115.The controller 120 has a detector circuit therein, to detect thecapacitance variations along the sensing lines X1, X2, . . . , Xm, . . ., XM and Y1, Y2, . . . , Yn, . . . , YN. The detected capacitancevariation is referred to as a sensed value, from which a position of anobject touched on the touch sensor 110 can be determined.

In further detail, as shown in FIG. 2, a sensing line has manycapacitive sensor pads 130 to 148 thereon. If this sensing line has animpedance so low as to be negligible, the sensed values generated by anobject touch on anywhere of the sensor pads 130 to 148 are substantiallyequal, and allow the controller 120 to precisely determine, according topreset reference values, whether or not an object touch has been made.On the contrary, if the electric resistance of this sensing line is toolarge to be ignored, the sensing line of FIG. 2 will have an equivalentcircuit as shown in FIG. 3, which will produce a resistor-capacitor (RC)filtering effect on the sensed values generated therefrom. As a result,referring to FIG. 4, when an object touches the sensing line atdifferent sensor pads 130 to 148, the sensed values detected by thecontroller 120 will be different from each other and are attenuated withthe distance between the controller 120 and the touched sensor pads 130to 148. Consequently, there is a great difference between the sensedvalue corresponding to the nearest sensor pad 130, which is adjacent tothe controller 120, and the sensed value corresponding to the farthestsensor pad 148, which is away from the controller 120. The attenuationof the sensed values due to actual impedance makes it difficult to makeadjustments to the capacitive touchpad, or even impossible to detect acapacitance variation if a thicker medium is used in the touchpad.Moreover, even if an object touches a same sensing line, the sensedvalues corresponding to different sensor pads may be so significantlyvaried as to increase the chances of error actions resulted frommisjudgments by the controller.

The problem resulted from the attenuation of the sensed values due tothe impedance of a sensing line itself can be minimized by arranging allthe sensing lines of a capacitive touchpad in an interleaving manner soas to homogenize the resistance/capacitance distribution of the sensinglines. However, for interleaving sensing lines arrangement, the sensinglines in X and Y directions are drawn to the controller from twoopposite ends thereof and result in a rather complicated wiring layout.Moreover, as shown in FIG. 5, if a touch sensor 210 has a rectangularshape, and the sensing lines in X and Y directions are drawn to acontroller 220 from two opposite ends thereof, the excessively longsensing lines 230 to 234 not only increase the difficulty in wiringlayout, but also produce additional parasitic resistances, which willfurther increase the difficulty in signal processing as well.

SUMMARY OF THE INVENTION

An object of the present invention is to provide an equalized capacitivetouchpad and a touch positioning method for a capacitive touchpad.

Another object of the present invention is to provide an apparatus andmethod for simplifying the wiring layout of a capacitive touchpad.

Yet another object of the present invention is to provide an apparatusand method for improving the touch positioning accuracy of a capacitivetouchpad.

According to the present invention, an equalized capacitive touchpad anda touch positioning method use an equalizer to correct a sensed valuedetected from a sensing line to offset the attenuation of the sensedvalue due to the impedance of the sensing line. Thus, the sensed valuesgenerated from different positions along a sensing line are equalizedand the touch positioning accuracy of the capacitive touchpad isimproved.

A capacitive touchpad according to the present invention includes atouch sensor having a plurality of sensing lines connected to acontroller which has a front-end circuit for scanning the sensing linesto generate sensed values.

Preferably, a sensed value in a first direction is used to determine aposition information in the first direction for the equalizer todetermine an equalization value according to an equalize function for asecond direction, which is used to correct a sensed value in the seconddirection.

Preferably, the equalizer has a memory for storing the equalizationvalue of the equalize function.

Preferably, the sensing lines in the first direction have a balancedresistance/capacitance distribution.

According to the present invention, an equalized capacitive touchpad anda touch positioning method use an equalizer to correct a sensed value ofa mutual capacitance between two sensing lines to offset the attenuationof the sensed value due to the impedance of the sensing lines. Thus, thesensed values of the mutual capacitances generated from differentpositions along a sensing line are equalized and the touch positioningaccuracy of the capacitive touchpad is improved. The equalizedcapacitive touchpad includes a touch sensor and a controller, the touchsensor includes a plurality of sensing lines connected to thecontroller, and the controller includes a front-end circuit to sense themutual capacitance between two of the plurality of sensing lines togenerate a sensed value.

BRIEF DESCRIPTION OF THE DRAWINGS

These and other objects, features and advantages of the presentinvention will become apparent to those skilled in the art uponconsideration of the following description of the preferred embodimentsof the present invention taken in conjunction with the accompanyingdrawings, in which:

FIG. 1 is a schematic view of a typical capacitive touchpad;

FIG. 2 is a schematic view of the structure of a typical sensing line;

FIG. 3 is the equivalent circuit of the sensing line shown in FIG. 2;

FIG. 4 is a schematic diagram showing the distribution of sensed valuesgenerated by touching the sensing line of FIG. 2 at different positionsthereof;

FIG. 5 is a schematic view of a capacitive touchpad having a rectangulartouch sensor and interleaving sensing lines;

FIG. 6 is a diagram depicting the principle of the present invention toequalize the sensed values of a sensing line of a capacitive touchpad;

FIG. 7 a functional block diagram of a capacitive touchpad and aflowchart of a touch positioning method for the capacitive touchpad inan embodiment according to the present invention;

FIG. 8 is a schematic diagram showing the sensed values generated from atouch sensor that is touched at different times under a same condition;

FIG. 9 is a diagram showing an embodiment of the equalizer according tothe present invention;

FIG. 10 is a diagram showing a first embodiment of the wiring layout ofa touch sensor;

FIG. 11 is a diagram showing a second embodiment of the wiring layout ofa touch sensor;

FIG. 12 is a diagram showing a third embodiment of the wiring layout ofa touch sensor;

FIG. 13 is a diagram showing a fourth embodiment of the wiring layout ofa touch sensor;

FIG. 14 is a schematic diagram showing some mutual capacitances betweensome sensing lines in an X direction and some sensing lines in a Ydirection;

FIG. 15 is a diagram depicting a method of sensing a mutual capacitancebetween a sensing line in an X direction and a sensing line in a Ydirection;

FIG. 16 is a schematic diagram showing an equivalent circuit of asensing line in a Y direction and the mutual capacitances sensed fromthis sensing line when it is touched at different positions;

FIG. 17 is a schematic diagram showing a distribution of sensed mutualcapacitances when a touch sensor is not touched;

FIG. 18 is a schematic diagram showing an equalize function designed forthe distribution of the sensed values shown in FIG. 17;

FIG. 19 is a diagram depicting the principle of the present invention toequalize the sensed values shown in FIG. 17;

FIG. 20 is a diagram showing a wiring layout of sensing lines in an Xdirection;

FIG. 21 is a diagram showing a wiring layout of sensing lines in a Ydirection;

FIG. 22 is a diagram showing a fifth embodiment of a wiring layout of atouch sensor; and

FIG. 23 is an equivalent circuit of the sensing line shown in FIG. 22.

DETAILED DESCRIPTION OF THE INVENTION

FIG. 6 depicts the principle of the present invention to equalize thesensed values of a sensing line of a capacitive touchpad. Taking thetouch sensor 110 shown in FIG. 1 for example, the sensing lines X1, X2,. . . , Xm, . . . , XM in the X direction are orthogonal to the sensinglines Y1, Y2, . . . , Yn, . . . , YN in the Y direction. Therefore,positions on the sensing line Xm in the X direction can be defined bythe positions y1, y2 . . . , yN of the sensing lines Y1, Y2, . . . , Yn,. . . , YN in the Y direction, as shown by the horizontal coordinates inFIG. 6. The vertical coordinates in FIG. 6 represent theanalog-to-digital converter (ADC) counts, which are used to denote thesensed values detected by the controller 120 from the sensing lines of ageneral capacitive touchpad, and the ADC counts signify the magnitudesof capacitance variation along a particular sensing line. As shown by acurve 310 in FIG. 6, if the sensing line Xm has a significantresistance, the sensed value detected by the controller 120 willattenuate as the distance between the controller 120 and the touch pointincreases and as a result, the sensed value corresponding to theposition y1 on the sensing line Xm will be lower than the sensed valuecorresponding to the position yN. An equalize function according to thepresent invention is shown by a curve 320, and has the equalizationvalues corresponding to each of the positions y1, y2 . . . , yN tocorrect the sensed values corresponding thereto to thereby offset theattenuation effect. A processing unit 340 may correct the curve 310according to the equalize function represented by the curve 320 to be anequalized curve 330. Actually, the structure of the sensing line Xm isnot changed, and the original sensed values generated therefrom stillfollow the curve 310. However, the sensed values actually detected by acontroller are calibrated by a pertinent software or hardware such thatthe sensed values corresponding to touches at positions y1, y2, . . . ,yN on the sensing line Xm are all equal to a certain value S as shown bythe curve 330. In an embodiment, the equalize function represented bythe curve 320 is obtained from calculation based on the equivalentcircuit shown in FIG. 3. In another embodiment, the equalize functionrepresented by the curve 320 is deduced from the sensed values actuallydetected from the sensing line Xm.

In some other embodiments, the sensing lines may be arranged indirections other than the X and Y directions. In some other embodiments,the sensing lines are not necessarily divided into two groups that areorthogonal to each other, but two groups that intersect each other suchthat either one of the two groups can be used to define differentpositions on any single sensing line in the other group. The sensinglines in the embodiments hereinafter are arranged in the orthogonal Xand Y directions to facilitate explanation so that features of thepresent invention can be more readily understood.

FIG. 7 shows a functional block diagram of a capacitive touchpad and aflowchart of a touch positioning method for the capacitive touchpad inan embodiment according to the present invention. For simplicity, it isassumed in this embodiment that the capacitive touchpad includes sensinglines in the Y direction having a balanced resistance/capacitancedistribution. In other words, the attenuation effect on the sensinglines in the Y direction is excluded. When an object 400 touches a touchsensor 410, a front-end circuit 420 generates a sensed value SX in the Xdirection and a sensed value SY in the Y direction by scanning thesensing lines. The sensed values SY in the Y direction corresponding totouches at different positions are invariant with respect to positionsof the object 400, while the sensed values SX in the X directionattenuate as the distance between the object 400 and the front-endcircuit 420 increases. A Y-direction positioning step 440 determines aY-direction position yn of the object 400 according to the sensed valueSY in the Y direction, and information of this Y-direction position ynis provided to an equalizer 430 for the X direction. Based on theY-direction position yn, the equalizer 430 determines an equalizationvalue K according to an equalize function, and then corrects the sensedvalue SX in the X direction to be a corrected sensed value S, from whichan X-direction positioning step 450 determines an X-direction positionXm of the object 400. The information of X-direction position Xm and theY-direction position yn as well as the sensed values S and SY of theobject 400 are provided to a post-processing step 460 for furtherprocessing, such as to determine a moving speed or an acceleration ofthe object 400. Operations in the Y-direction positioning step 440, theX-direction positioning step 450 and the post-processing step 460 are infact accomplished by the arithmetic unit of the controller and pertainto prior arts.

When different positions A, B, C and D in the Y direction at a sameposition in the X direction of the touch sensor 410 are touched atdifferent times under a same condition, the corresponding sensed valuesin the X and Y directions are shown in FIG. 8, in which the position Ahas the largest sensed value in the X direction, the position D has thesmallest sensed value in the X direction, and the sensed values in the Ydirection are not significantly varied with the different positions A,B, C and D. If the sensed values actually obtained are used for touchpositioning, it may be impossible to accurately determine the positionof each of A, B, C and D because the X-direction sensed valuescorresponding to the different positions A, B, C and D are great varied.If a user moves his finger from the position A to the positions B, C andD sequentially, the Y-direction sensed values clearly show a variationin the Y direction corresponding to contacts by the finger at the fourpositions, so that it can be further determined that the finger hasmoved in the Y direction. In the X direction, however, if the sensedvalues actually obtained are used for touch positioning, it may beimpossible to accurately determine that the finger has actually stayedat a same position in the X direction. Nevertheless, after applying theaforementioned equalization described with reference to FIG. 7, thecorrected X-direction sensed values will be able to clearly show achange of positions, as do the Y-direction sensed values.

The equalizer 430 can be realized by hardware, software or a combinationthereof, and an embodiment of the equalizer 430 is shown in FIG. 9, inwhich the sensing lines Y1, Y2, . . . , YN in the Y direction of thetouch sensor 410 have a balanced resistance/capacitance distribution,and the controller 120 includes the equalizer 430. As described above,the sensing lines Y1, Y2, . . . , YN in the Y direction having thebalanced resistance/capacitance distribution can be achieved with aninterleaving wiring layout. FIG. 10 is a diagram showing an example of awiring layout in which the sensing lines Y1, Y2, . . . , YN areinterleaving while the sensing lines X1, X2, . . . , XM in the Xdirection are arranged in a same direction. FIG. 11 is a diagram showinganother wiring layout in which the sensing lines Y1, Y2, . . . , YN inthe Y direction are arranged in a same direction and each of them has aU shape to achieve a balanced resistance/capacitance distribution, whilethe sensing lines X1, X2, . . . , XM in the X direction are stillarranged in a same direction. FIG. 12 is a diagram showing yet anotherwiring layout in which the sensing lines Y1, Y2, . . . , YN in the Ydirection are interleaving and each of them has a U shape to achieve abalanced resistance/capacitance distribution, while the sensing linesX1, X2, . . . , XM in the X direction are still arranged in a samedirection. The touch sensor 410 shown in FIG. 13 has a rectangularshape, and the sensing lines Y1, Y2, . . . , YN in the Y direction haveshorter lengths so as to reduce the resistor-capacitor (RC) filteringeffect to be one could be ignored, or could be eliminated with a circuitadjustment in order to equalize the sensed values thereof. On the otherhand, the sensed values from the sensing lines X1, X2, . . . , XM in theX direction in FIG. 13 can be equalized by applying the aforementionedequalization thereto. Hence, not only can the sensing lines X1, X2, . .. , XM be arranged in a same direction, but also the sensing lines Y1,Y2, . . . , YN can be arranged in a same direction, thereby simplifyingthe wiring layout of the sensing lines. Referring back to FIG. 9, thecontroller 120 includes the front-end circuit 420 and the equalizer 430that is realized by a combination of an arithmetic logic unit (ALU) 340and a memory 470. The memory 470 stores the equalize function for the Xdirection, so that the ALU 340 can extract from the memory 470 anequalization value K of the equalize function that corresponds to aY-direction position yn and thereby correct an X-direction sensed valueSX into S, from which an X-direction position Xm can be furtherdetermined. The equalize function can be stored in the memory 470 as alookup table where all the equalization values of the equalize equationare stored, so that the ALU 340 can read the equalization value K bylooking it up in the table. In another embodiment, the memory 470 maystore only a formula of the equalize function or certain parameters ofthe equalize function, with which the ALU 340 calculates data itreceives to generate corresponding equalization values of the equalizefunction. In the embodiment shown in FIG. 9, no physical wiring is addedto the controller 120, and operations of the equalizer 430 are executedby the ALU 340 and the memory 470 of the controller 120. Hence, no extracost of hardware is incurred.

As demonstrated by the foregoing embodiments, the wiring layout of thetouch sensor 410 can be simplified by properly arranging the sensinglines in the Y direction to eliminate variation resulted fromattenuation, and using the equalizer 430 to correct the sensed values inthe X direction.

Another advantage of using the equalizer 430 to correct the sensedvalues is ease of adjustment thereto. Although a designer of thecontroller 120 cannot control the degree of attenuation taking placealong the sensing lines of the touch sensor 410, the equalize functionstored in the controller 120 can be changed at any time, so that theequalize function in the controller 120 can be adjusted according to thetouch sensor 410 actually used. Thus, the controller 120 is adaptive tovarious touch sensors 410 having different specifications, which alsorelieves the designer of the controller 120 from an otherwise difficulttask.

In the touch sensor 410 shown in FIG. 9, between each of the sensinglines X1-XM in the X direction and each of the sensing lines Y1-YN inthe Y direction there is a mutual capacitance present, as indicative ofthe mutual capacitances CM,1, CM,2, CM-1,1, CM-1,2 in FIG. 14. If afinger touches the touch sensor 410 at the position of the coordinates(XM, Y1), the mutual capacitance CM,1 corresponding to the positionwhere the finger touches will change. Therefore, the front-end circuit420 may identify where the finger is by detecting the variations amongthe mutual capacitances of the sensing lines. FIG. 15 depicts a methodof sensing a mutual capacitance, in which the controller 120 applies asignal 500 by an output terminal to the sensing line XM in the Xdirection, the signal 500 will be coupled to the sensing line Y1 throughthe mutual capacitance CM,1 between the sensing lines XM and Y1 and thentransmitted to a receiving terminal of the controller 120 through thesensing line Y1, and the front-end circuit 420 inside the controller 120may calculate the sensed value of the mutual capacitance CM,1 accordingto the received signal. As shown in FIG. 4, when the signal 500 istransmitted along the sensing line XM in the X direction, it willundergo attenuation due to the resistor-capacitor (RC) filtering effectalong the sensing line XM. Similarly, after being coupled to the sensingline Y1 through the mutual capacitance CM,1, the signal 500 will undergoattenuation due to the resistor-capacitor (RC) filtering effect alongthe sensing line Y1 when it is transmitted to the receiving terminal ofthe controller 120 through the sensing line Y1. Therefore, as shown inFIG. 16, the sensed value detected by the controller 120 is attenuatedwith the distance between the controller 120 and the touched sensor pad502 to 520, and as a result, the closer to the receiving terminal of thecontroller 120 the finger is along the sensing line Y1, the more thesensed value is.

As described above, depending on the distance between the detectedposition and the output terminal of the controller and the distancebetween the receiving terminal and the detected position, the detectedsensed values show different levels of attenuation. FIG. 17 shows thesensed values of the mutual capacitances when the touch sensor 410 istouched, which have a stepped pattern of distribution in such a mannerthat the mutual capacitance closer to the controller 120 is related to agreater sensed value, and on the contrary, the mutual capacitance thatis more distant from the controller 120 has the sensed value smaller.Since the sensing lines X1-XM in the X direction and the sensing linesY1-YN in the Y direction are all subject to the resistor-capacitor (RC)filtering effect, gradient variations are present in the X direction andthe Y direction, respectively. According to the distribution of thesensed values shown in FIG. 17, an equalize function as shown in FIG. 18may be devised to compensate the resistor-capacitor (RC) filteringeffect. In this case, the equalizer 430 inside the controller 120,according to the detected position information of the mutualcapacitance, determines an equalization value from the equalize functionto correct the sensed value that has been detected, and then thecontroller 120 uses the corrected sensed value to determine whether andwhere the touch sensor 410 is touched. The position information of themutual capacitance includes the positions of the corresponding sensinglines in the X direction and in the Y direction. The equalizer 430 maybe realized as hardware, software or a combination of hardware andsoftware. For instance, the equalizer 430 shown in FIG. 9 is realized bythe ALU 340 and the memory 470, and the ALU 340 gets an equalizationvalue from the equalize function stored in the memory 470 according tothe position information of the detected mutual capacitance to correctthe corresponding sensed value. As shown in FIG. 19, when the touchsensor 410 is touched, the sensed values of all the positions that havebeen corrected are identical. The memory 470 may store the equalizefunction as a lookup table that contains all the equalization values ofthe equalize function, for the ALU 340 to look up the relevantequalization values. In other embodiments, the memory 470 may only storean equation or some certain parameters, for the ALU 340 to use the samein its calculation for an equalization value.

In the embodiment shown in FIG. 14, the mutually orthogonal sensinglines in the X and Y directions are described for easy illustration,while in other embodiments, the two groups of sensing lines mayintersect in a way other than being orthogonal to each other. Anyalternatives wherein the detection of touch positions by sensing mutualcapacitances may be feasible embodiments of the present invention.Additionally, in FIG. 14, each mutual capacitance is on the intersectionof two sensing lines running in two directions, while in otherembodiments, for example in applications of spiral sensing lines, wherethe sensing lines running in two directions do not intersect, the mutualcapacitance between two sensing lines running in two directions is atthe handshaking site of the two sensing lines.

FIG. 20 and FIG. 21 show wiring layouts helping to reduce theresistor-capacitor (RC) filtering effect in the course of detectingmutual capacitances, in which each of the sensing lines X1-XM in the Xdirection has its both ends connected to a respective output terminal ofthe controller 120, and each of the sensing lines Y1-YN in the Ydirection has its both ends connected to a respective receiving terminalof the controller 120. Taking the sensing lines X1 and Y1 for example,when an output terminal of the controller 120 transmits a signal 500,the signal 500 will be applied to the two ends of the sensing line X1 atthe same time. For the signal 500, the impedance on the sensing line X1is halved from its original size, so the resistor-capacitor (RC)filtering effect acting on the sensing line X1 is reduced. Similarly,the controller 120 receives the signal 500 froth the both ends of thesensing line Y1 and thus, for the signal 500, the impedance on thesensing line Y1 is also half of its original size, causing theresistor-capacitor (RC) filtering effect acting on the sensing line Y1to be reduced.

FIG. 22 is another wiring layout helpful to reduce theresistor-capacitor (RC) filtering effect. Again taking the sensing linesX1 and Y1 for example, instead of having the sensing lines X1 and Y1 asserially connected diamond capacitive sensor pads 130-148 and 502-520 asshown in FIG. 1, FIG. 2, and FIG. 16, this embodiment has each of thediamond capacitive sensor pads on the sensing line X1 halved into aright and a left triangular capacitive sensor pads, the left triangularcapacitive sensor pads are serially connected into a sub-sensing lineX11, the right triangular capacitive sensor pads are serially connectedinto a sub-sensing line X12, and the sub-sensing lines X11 and X12 areconnected in parallel into the sensing line X1. Similarly, each of thediamond capacitive sensor pads in the sensing line Y1 is halved into anupper and a lower triangular capacitive sensor pads, the uppertriangular capacitive sensor pads are serially connected into asub-sensing line Y11, the lower triangular capacitive sensor pads areserially connected into a sub-sensing line Y12, and the sub-sensinglines Y11 and Y12 are connected in parallel into the sensing line Y1.FIG. 23 is the equivalent circuit of the sensing line X1 or Y1 shown inFIG. 22. Since the sensing lines X1 and Y1 shown in FIG. 22 are halvedand connected in parallel, as compared to the sensing lines X1 and Y1formed by a plurality of serially connected diamond capacitive sensorpads, their impedance levels are reduced by more than half, beingeffective in lowering the resistor-capacitor (RC) filtering effect.

While the present invention has been described in conjunction withpreferred embodiments thereof, it is evident that many alternatives,modifications and variations will be apparent to those skilled in theart. Accordingly, it is intended to embrace all such alternatives,modifications and variations that fall within the spirit and scopethereof as set forth in the appended claims.

What is claimed is:
 1. An equalized capacitive touchpad, comprising: atouch sensor having M first sensing lines in a first direction and Nsecond sensing lines in a second direction with M×N mutual capacitancestherebetween, where M and N are integers larger than one; a controllercoupled to the N second sensing lines, the controller comprising afront-end circuit for detecting the M×N mutual capacitances to generateM×N sensed values; and an equalizer coupled to the front-end circuit,having M×N equalization values respectively corresponding to the M×Nmutual capacitances between the M first sensing lines and the N secondsensing lines, for determining a corresponding equalization valueaccording to position information of a detected mutual capacitance, andcorrecting the sensed value with the corresponding equalization value toobtain a corrected sensed value; wherein the equalization values are forcompensating for resistor-capacitance filtering effect, and thecorresponding equalization value increases as the detected mutualcapacitance is more distant from the controller; and wherein thecorrected sensed value is used to determine a touched position.
 2. Theequalized capacitive touchpad of claim 1, wherein the equalizercomprises: a memory storing an equalize function; and an arithmeticlogic unit coupled to the memory, determining the correspondingequalization value according to the equalize function and the positioninformation of the detected mutual capacitance.
 3. The equalizedcapacitive touchpad of claim 1, wherein the controller is coupled to twoends of each of the M first sensing lines.
 4. The equalized capacitivetouchpad of claim 3, wherein the controller is coupled to two ends ofeach of the N second sensing lines.
 5. The equalized capacitive touchpadof claim 1, wherein each of the M first sensing lines comprises twosub-sensing lines connected in parallel and each of the two sub-sensinglines has a plurality of capacitive sensor pads.
 6. The equalizedcapacitive touchpad of claim 1, wherein each of the N second sensinglines comprises two sub-sensing lines connected in parallel and each ofthe two sub-sensing lines has a plurality of capacitive sensor pads. 7.The equalized capacitive touchpad of claim 1, wherein the M firstsensing lines and the N second sensing lines are transparent.
 8. Theequalized capacitive touchpad of claim 1, wherein the M first sensinglines and the N second sensing lines are made of an indium tin oxide,indium zinc oxide, carbon paste or silver ink.
 9. The equalizedcapacitive touchpad of claim 1, wherein the M first sensing lines andthe N second sensing lines intersect with each other.
 10. The equalizedcapacitive touchpad of claim 1, wherein the M first sensing lines andthe N second sensing line intersect with each other orthogonally.
 11. Atouch positioning method for a capacitive touchpad, comprising the stepsof: detecting a plurality of mutual capacitances respectively formedbetween a plurality of first sensing lines and a plurality of secondsensing lines by a controller to generate a plurality of sensed values;determining a corresponding equalization value according to positioninformation of a detected mutual capacitance; correcting the sensedvalue with the corresponding equalization value to obtain a correctedsensed value; and identifying a touched position according to thecorrected sensed value; wherein the equalizations values associated withthe mutual capacitances are for compensating for resistor-capacitancefiltering effect, and the corresponding equalization value increases asthe detected mutual capacitance is more distant from the controller. 12.The touch positioning method of claim 11, wherein the step ofdetermining the corresponding equalization value: storing an equalizefunction in advance; and determining the equalization value according tothe equalize function and the position information of the detectedmutual capacitance.
 13. The touch positioning method of claim 11,wherein the step of detecting the plurality of mutual capacitancescomprises the steps of: sequentially applying a first signal to each ofthe plurality of first sensing lines; receiving a second signal fromeach of the plurality of second sensing lines; and determining theplurality of sensed values from the second signal.